TheHitchhikers GuideTo The Galaxy

Earth Edition

How a Nuclear Plant Works

Nuclear power is one of the most controversial subjects in today's world. Five decades of nuclear threat plus countless bad horror movies have lead the general public to believe everything nuclear or radioactive is negative; up to and including nuclear power plants. Because of this, the average layman is unaware of how a nuclear power plant works, or what it does, except make nuclear waste.

Basic Workings

The function of a nuclear power plant is to make electricity. It does this the same way as coal, oil, and natural gas power plants do; namely, it heats water into steam in order to turn a generator. The difference is the way that it heats water.

Instead of burning fossil fuel, a reactor will heat water by bringing pellets of uranium close together until they form a critical mass. When uranium decays, neutrons and heat are released. If enough uranium is near by, then the neutrons will run into other uranium atoms, causing them to split apart, or fission, and release more neutrons and more heat. Nuclear reactors submerge the fissioning uranium in water. The fuel heats up the water, and the water boils and turns to high pressure steam, which turns the turbine.

Boiling Water Reactors vs Pressurized Water Reactors

There are two main types of reactors in use today: Boiling Water Reactors (BWRs) and Pressurized Water Reactors (PWRs).

In PWRs, the reactor and associated pipes and pumps are called the Reactor Coolant System (RCS), or the 'Primary Loop'. The RCS is a closed system in that nothing in the system is allowed to escape during normal operation, as it would be radioactive. Water in the RCS is not allowed to boil. Instead, the water is pressurized to prevent it from boiling. While pressurized, the water can now be heated to a temperature of several hundred degrees, and is sent to a steam generator.

The steam generator has two types of water in it: primary loop water, and secondary loop water. The two types of water are never allowed to mix. The primary water enters the steam generator through hundreds of small tubes. The tubes heat up and causes the secondary water to boil and turn to high pressure steam, which is used to turn the turbine and create electricity. The advantage of PWRs is that the RCS is the only part of the plant that is radioactive.

In BWRs, water in the RCS is boiled directly. The RCS water itself is turned to steam and is used to turn the turbine. The advantage of this system is that there are no steam generators involved, which means that there is less complexity, fewer components, and less maintenance to perform. The disadvantage is that the turbine is now contaminated with radioactivity.

Advantages of Nuclear Power

Nuclear power is relatively efficient. Most nuclear reactors only need to be refueled every 18 months or so. At each refueling, a third of the fuel is removed and stored as waste, and new fuel is inserted in its place. The new fuel costs about US$40 to $60 million per refueling. By contrast, a similarly sized natural gas power plant can consume up to $600 million in natural gas over the same time period. A similarly sized coal plant would require at least a dozen large dump trucks full of coal each day.

Also, since nuclear power plants do not burn anything, they do not generate air pollution the same way fossil fuel plants do.

Disadvantages of Nuclear Power

When uranium fuel is used up (or becomes 'spent'), it becomes highly radioactive1. So much so that anyone standing unprotected near a spent fuel assembly will contract a lethal dose of radiation in minutes. The only way that has been proposed to dispose of this spent fuel is to bury it and wait for the radiation to fade away, which could take thousands of years2. Of course, no man-made structure is known to have remained intact for such a long period, so practically speaking, the disposal problem remains unsolved.

Nuclear plants require at least five to ten times as many personnel to operate as fossil plants. This is due to the complexity of a nuclear plant, as well as the nature of government regulation3 of nuclear power. Lots and lots of manpower is required to fulfil government regulatory requirements.

Nuclear plants are also much less forgiving than conventional plants. The difference between a nuclear plant and a conventional fossil plant can be illustrated by comparing a high-performance fighter jet to an airliner. A person can take his hands off the control yoke of an airliner and go quite some way before getting in trouble, but if a fighter pilot takes his hands of the control stick, the fighter will quickly crash. Similarly, a moment of sloppiness or inattention when operating a nuclear plant could very possibly cause a very severe accident, such as the reactor explosion at Chernobyl, Ukraine in 1986 or the partial meltdown at Three Mile Island in Middletown, Pennsylvania, USA4.

1Although radioactive fission products are produced, they are the only radioactive part of the fuel assembly, and are mixed in with everything else.2Some countries reprocess their spent fuel, which means removing and disposing of the radioactive portion of the waste and recycling the non-radioactive portion into new fuel assemblies. While this reduces the volume of waste (as the highly radioactive matter is no longer mixed with non-radioactive matter), there still remains the problem of disposing of the radioactive part. Also, reprocessing plants have historically had numerous operating and radiological problems, some even occasionally releasing radiation into the environment.3Most Western nations heavily regulate nuclear power.4At Chernobyl, a dangerous experiment involving running a steam power turbine using decay heat, instead of full power heat, resulted in a reactor explosion and fire which spewed radioactive smoke into the atmosphere for days. At Three Mile Island, a spurious activation of a valve caused a chain of events eventually leading to a radioactive release of water and a partial melting of the fuel in the reactor core.

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